Super-elastic titanium alloy for medical uses

ABSTRACT

A super-elastic titanium alloy for medical use consisting essentially of: molybdenum (Mo) as a β stabilizer element of titanium (Ti): from 2 to 12 at %; an α stabilizer element of the titanium (Ti): from 0.1 to 14 at %; and the balance being titanium (Ti) and inevitable impurities. The α stabilizer element is at least one element selected from the group consisting of aluminum (Al), gallium (Ga) and germanium (Ge).

CROSS REFERENCE

This application is a divisional of copending U.S. patent applicationSer. No. 10/396,917 filed on Mar. 25, 2003.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a super-elastic Ti alloy for medicaluses. Particularly, the present invention relates to a Ti—Mo—Ga alloy, aTi—Mo—Al alloy and a Ti—Mo—Ge alloy which exhibit super elasticproperties and which are useful for medical applications.

2. Related art

Recently, many attempts have been made to find medical applications ofan alloy with a super elastic property. For example, a Ti—Ni alloy hasproperties of high strength, excellent abrasion resistance, goodcorrosion resistance, good biocompatibility and the like, and is used ina variety of fields as an alloy for medical uses.

As an example, a Ti—Ni alloy wire used in an orthodontic appliance has asuper-elastic region where constant loading is maintained irrespectiveof changes in deformation of the wire. Since this wire can impartnecessary forces constantly even after teeth are moved byteeth-straightening, it is usable as an orthodontic wire. In addition,such a alloy is also usable in implants for plastic surgery with thefull use of its excellent recoverability, and usable for medicalcatheters, guide wires or the like with the full use of its reasonableformability and stiffness.

Such a Ni—Ti alloy is described in the Japanese Provisional PatentPublication No. 5-295498, which consists of from 49.5 to 51.5% Ni, 1.8%or less Cr and the balance Ti. This alloy is made by casting, hotworking and then, repeating annealing and cold working.

In these days, concerns are rising over biomedical materials having a Nimetal which, suspected of causing allergic symptom, may be leached outwithin the living body. Since a Ni—Ti alloy contains Ni as a principalelement, the Ni—Ti alloy may cause anxiety about allergy, and therefore,demands for safer alloys usable in medical applications are growing.

In other words, demands are growing for alloys which contain no elementsuch as Ni that may cause an allergic problem to the living body buthave good biocompatibility.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a Ni-free alloywhich is useful for medical applications, or a titanium alloy which hasimproved biocompatibility as well as super-elastic properties.

A first embodiment of the super-elastic titanium alloy for medical usesof the present invention is a super-elastic titanium alloy for medicaluse consisting essentially of:

-   -   molybdenum (Mo) as a β stabilizer element of titanium (Ti)        -   : from 2 to 12 at %;    -   an α stabilizer element of the titanium (Ti)        -   : from 0.1 to 14 at %; and    -   the balance being titanium (Ti) and inevitable impurities.

A second embodiment of the super-elastic titanium alloy for medical usesof the present invention is a super-elastic titanium alloy in which saidα stabilizer element is at least one element selected from the groupconsisting of aluminum (Al), gallium (Ga) and germanium (Ge).

A third embodiment of the super-elastic titanium alloy for medical usesof the present invention is a super-elastic titanium alloy in which saidα stabilizer element is from 0.1 to 14 at % gallium (Ga).

A fourth embodiment of the super-elastic titanium alloy for medical usesof the present invention is a super-elastic titanium alloy in which saidα stabilizer element is from 3 to 14 at % aluminum (Al).

A fifth embodiment of the super-elastic titanium alloy for medical usesof the present invention is a super-elastic titanium alloy in which saidα stabilizer element is from 0.1 to 8 at % germanium (Ge).

A sixth embodiment of the super-elastic titanium alloy for medical usesof the present invention is a super-elastic titanium alloy in which saidα stabilizer element is from 3 to 9 at % aluminum (Al) and a content ofsaid molybdenum (Mo) is from 4 to 7 at %.

A seventh embodiment of the super-elastic titanium alloy for medicaluses of the present invention is a super-elastic titanium alloy asclaimed in claim 2, wherein said α stabilizer element is from 1 to 4 at% gallium (Ga) and a content of said molybdenum (Mo) is from 4 to 7 at%.

An eighth embodiment of the super-elastic titanium alloy for medicaluses of the present invention is a super-elastic titanium alloy in whichsaid α stabilizer element is from 1 to 4 at % germanium (Ge) and acontent of said molybdenum (Mo) is from 4 to 7 at %.

A ninth embodiment of the super-elastic titanium alloy for medical usesof the present invention is a super-elastic titanium alloy in which saidsuper-elastic titanium alloy is a β solid solution titanium alloy havingan orthorhombic crystalline structure.

A first embodiment of a method for making a super-elastic titanium alloyfor medical use of the present invention is a method for making asuper-elastic titanium alloy for medical use comprising the steps of:

-   -   preparing a titanium alloy ingot which consists essentially of:        -   molybdenum (Mo) as a β stabilizer element of titanium (Ti)            -   : from 2 to 12 at %;        -   as an α stabilizer element of the titanium (Ti), at least            one element selected from the group consisting of aluminum            (Al), gallium (Ga) and germanium (Ge)            -   : from 0.1 to 14 at %; and        -   the balance being titanium (Ti) and inevitable impurities,    -   subjecting the ingot to a homogenized heat treatment in a vacuum        environment or an inert gas environment at a temperature ranging        from 1,000 degree to 1,200 degree, and cooling the ingot quickly        to a room temperature;    -   after cooling the ingot to the room temperature, cold working        the ingot to prepare a sheet; and    -   subjecting the sheet to a solution heat treatment in the vacuum        environment or the inert gas environment at a temperature        ranging from 600 degree to 1,100 degree.

A second embodiment of the method for making a super-elastic titaniumalloy for medical use of the present invention is a method in which theα stabilizer element of the titanium alloy ingot is from 0.1 to 14 at %gallium (Ga).

A third embodiment of the method for making a super-elastic titaniumalloy for medical use of the present invention is a method in which theα stabilizer element of the titanium alloy ingot is from 3 to 14 at %aluminum (Al).

A fourth embodiment of the method for making a super-elastic titaniumalloy for medical use of the present invention is a method in which theα stabilizer element of the titanium alloy ingot is from 0.1 to 8 at %germanium (Ge).

A fifth embodiment of the method for making a super-elastic titaniumalloy for medical use of the present invention is a method in which acontent of the molybdenum (Mo) is from 4 to 7 at % and the α stabilizerelement of the titanium alloy ingot is from 3 to 9 at % aluminum (Al).

A sixth embodiment of the method for making a super-elastic titaniumalloy for medical use of the present invention is a method in which acontent of the molybdenum (Mo) is from 4 to 7 at % and the α stabilizerelement of the titanium alloy ingot is from 1 to 4 at % gallium (Ga).

A seventh embodiment of the method for making a super-elastic titaniumalloy for medical use of the present invention is a method in which acontent of the molybdenum (Mo) is from 4 to 7 at % and the α stabilizerelement of the titanium alloy ingot is from 1 to 4 at % germanium (Ge).

An eighth embodiment of the method for making a super-elastic titaniumalloy for medical use of the present invention is a method in which atime of the homogenized heat treatment ranges from 10 to 48 hours.

A ninth embodiment of the method for making a super-elastic titaniumalloy for medical use of the present invention is a method in which atime of the solution heat treatment ranges from 1 minute to 10 hours.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view for explaining how to measure a bend angle;

FIG. 2 is a table which provides a listing of compositions of a Ti—Mo—Gaalloy and their evaluations;

FIG. 3 is a table which provides a listing of compositions of a Ti—Mo—Alalloy and their evaluations; and

FIG. 4 is a table which provides a listing of compositions of a Ti—Mo—Gealloy and their evaluations.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be described in detail below.An alloy of the present invention is a titanium alloy which, in order torealize thermo-elastic martensite transformation, contains alloyingelements of: molybdenum (Mo) which is a β stabilizer element forlowering a martensite transformation temperature; and at least oneselected from the group consisting of gallium (Ga), aluminum (Al) andgermanium (Ge) which are α stabilizer elements, or more specifically, asuper-elastic titanium alloy for medical uses to be substituted for aTi—Ni alloy.

Here, a β stabilizer element of the present invention is not limited toMo, but may be any β stabilizer element that can lower a martensitetransformation temperature. For example, elements such as niobium (Nb),Fe and the like can be replaced for Mo to obtain a super-elastictitanium alloy. Besides, an α stabilizer element is not limited to Ga,Al or Ge but may be tin (Sn), oxygen (O) or the like to obtain asuper-elastic titanium alloy.

Conventional Ni—Ti alloys are shape memory alloys having “shape memoryeffects” such that when an alloy having a certain shape is transformedto a different shape from the original shape at a lower temperature, andthen heated above a temperature for stabilizing a high temperature phase(parent phase, here), the reverse transformation (phase transformationassociated with heating and unloading) occurs and thereby, the alloyrecovers the original shape.

All alloys that undergo martensite transformation do not exhibit shapememory effects. Alloys that undergo thermo-elastic martensitetransformation (i.e., Ni—Ti alloys are included) recover their originalshapes upon heating as far as the deformation appears within certainlimits. Alloys according to the present invention are titanium alloyshaving such a property, or more specifically, titanium alloys to whichMo is added, and Ga, Al or Ge is further added thereto.

As one embodiment of the present invention a Ti—Mo—Ga alloy is nowdescribed. When Mo as an β stabilizer element is added to Ti, atemperature of a phase/β phase transformation is shifted toward a lowertemperature side, which allows to obtain an alloy with a stable β phasestructure even at room temperature. This is because rapid cooling from aβ phase temperature causes the β phase to be remained, and for the caseof a homogeneous solid-solution type binary Mo—Ti alloy, Mo content issaid to be about 20 at % at the minimum. For the case of an alloy withMo content about 20 at % or less, there occurs martensite transformationeven if the alloy is rapidly cooled, thus it cannot be said that the βphase is completely remained.

Such a martensite has two types of α phase, that is, α′ phase and α″phase, of which crystalline structures are hexagonal and orthorhombic,respectively. In order for an alloy to exhibit super-elastic effects,the martensite transformation has to be thermo-elastic martensitetransformation. Between these two martensitic α phases, the α″ phase isknown as one capable of being thermo-elastic martensite transformation.

When Ga is added to Ti, it is said that Ga functions as an α stabilizerelement, extending α phase region so as to improve the strength at roomtemperature. Then, development work has been advanced on super-elastic βphase type solid solution titanium alloys having the composition of Tito which Mo as a β stabilizer element for lowering martensitetransformation temperature and Ga as a α stabilizer element are added,which undergoes thermo-elastic martensite transformation upon rapidcooling. As a result, the super-elastic β phase type solid solutiontitanium alloys with the composition mentioned below has been developed.

In the present invention, Mo content is limited within the range of from2 to 12 at %. This is because the super elastic performance isdeteriorated when Mo content is below 2 at % or over 12 at %. In otherwords, there occurs plastic deformation within a deformed alloy, whichmakes it difficult for the alloy to recover its original shape.Preferable Mo content is within the range of from 4 to 7 at %. Morepreferably, Mo content is within the range of from 5 to 6 at %.

Ga content as an α stabilizer element is limited within the range offrom 0.1 to 14 at %. This is because super elastic performance isdeteriorated when Ga content is below 0.1 at % or over 14 at %. In otherwords, there occurs plastic deformation within a deformed alloy, whichmakes it difficult for the alloy to recover its original shape.Preferable Ga content is within the range of from 1 to 4 at %. Morepreferably, Ga content is within the range of from 3 to 4 at %.

Accordingly, a Ti alloy containing Mo from 2 to 12 at % and Ga from 1 to14 at % becomes a super-elastic β phase type solid solution titaniumalloy. Therefore, a crystalline structure of the rapidly cooled titaniumalloy becomes orthorhombic with excellent transformation behavior, whichfacilitates hot working and cold working, thereby reducing working costas compared with Ni—Ti alloys. A method for manufacturing a Ti—Mo—Gaalloy is described below as one example, however, this is not forlimiting the scope of the present invention.

First, metals as given alloying components are melted in a consumableelectrode arc melting furnace and cast into required shapes to prepareingots. Then, in order to remove segregation, thus prepared ingots aresubjected to homogenized heat treatment under the following conditions.Heat treatment environments are preferably vacuum or inert gasenvironments. Heat treatment temperatures preferably ranges from 1,000degree to 1,200 degree. Regarding heat treatment time, retention time isset within the range of from 10 to 48 hours. After being homogenizedheat treated, the ingots were rapidly cooled down to a room temperaturewith the use of oil or water.

The above-mentioned conditions for homogenized heat treatment areselected for the following reasons. The vacuum and inert gasenvironments are selected for preventing Ti from reacting to oxygen soas to avoid embrittlement of Ti. In addition, homogenized heat treatmentperformed below 1,000 degree may cause insufficient homogenization,while homogenized heat treatment performed over 1,200 degree may causepartial melting due to the too high temperature, reducing economicefficiency. When the retention time of less than 10 hours may causeinsufficient homogenization while the retention time of more than 48hours may reduce economic efficiency.

Then, the heat treated and rapidly cooled ingots are cold worked toprepare thin sheets. For the purpose of solid solution heat treatment ofalloying elements, the thin sheets are subjected to solution heattreatment under the following conditions. Heat treatment environmentsare preferably vacuum or inert gas environments. Heat treatmenttemperatures preferably ranges from 600 degree to 1,200 degree.Regarding heat treatment time, retention time is set within the range offrom 1 minute to 10 hours.

The above-mentioned conditions for solution heat treatment are selectedfor the following reasons. The vacuum and inert gas environments areselected for preventing Ti from reacting to oxygen so as to avoidembrittlement of Ti. In addition, heat treatment temperatures performedbelow 600 degree may cause insufficient heat treatment whiletemperatures over 1200 degree may reduce economic efficiency. When theretention time of less than 1 minute may cause insufficient heattreatment while the retention time of more than 10 hours may reduceeconomic efficiency. Then, appropriate working or heat treatment areperformed to obtain super-elastic titanium alloy with α phase finelyprecipitated.

As another embodiment of the present invention a Ti—Mo—Al alloy is nowdescribed. Effects of Mo added to Ti are the same as described in theabove embodiment.

When Al is added to Ti, Al functions as an α stabilizer element,extending α phase region so as to improve the strength at roomtemperature. Then, development work has been advanced on super-elastic βsolid solution titanium alloys having the composition of Ti to which Moas a β stabilizer element for lowering martensite transformationtemperature and Al as a α stabilizer element are added, which undergoesthermo-elastic martensite transformation upon rapid cooling. As aresult, the super-elastic β solid solution titanium alloys with thecomposition mentioned below has been developed.

Mo content as a β stabilizer element is limited within the range of from2 to 12 at %. This is because the super elastic performance isdeteriorated when Mo content is below 2 at % or over 12 at %. In otherwords, there occurs plastic deformation within a deformed alloy, whichmakes it difficult for the alloy to recover its original shape. Asdescribed above, preferable Mo content is within the range of from 4 to7 at %. More preferably, Mo content is within the range of from 5 to 6at %.

Al content as an α stabilizer element is limited within the range offrom 3 to 14 at %. This is because the super elastic performance isdeteriorated when Al content is below 3 at % or over 14 at %. In otherwords, there occurs plastic deformation within a deformed alloy, whichmakes it difficult for the alloy to recover its original shape.Preferable Al content is within the range of from 3 to 9 at %. Morepreferably, Al content is within the range of from 7 to 9 at %.

Accordingly, a Ti alloy containing Mo from 2 to 12 at % and Al from 3 to14 at % becomes a super-elastic β solid solution titanium alloy.Therefore, a crystalline structure of the rapidly cooled titanium alloybecomes orthorhombic with excellent transformation behavior, whichfacilitates hot working and cold working, thereby reducing working costas compared with Ni—Ti alloys.

Such a Ti—Mo—Al alloy can be manufactured in the same method as that forthe aforementioned Ti—Mo—Ga alloy, though the present invention is notlimited to this method. In the other words, metals as given alloyingcomponents are melted in a consumable electrode arc melting furnace, andcast into required shapes to prepare ingots. Then, in order to removesegregation, thus prepared ingots are subjected to homogenized heattreatment under the conditions that heat treatment environments arepreferably vacuum or inert gas environments, heat treatment temperaturespreferably range from 1,000 degree to 1,200 degree and the retentiontime was set within the range of from 10 to 48 hours. After beinghomogenized heat treated, the ingots are rapidly cooled down to a roomtemperature with the use of oil or water.

The ingots are cold worked to prepare thin sheets. For the purpose ofsolution heat treatment of alloying elements, the thin sheets aresubjected to solution heat treatment under the following conditions thatheat treatment environments are preferably vacuum or inert gasenvironments, heat treatment temperatures preferably ranges from 600degree to 1,100 degree and retention time is set within the range offrom 1 minute to 10 hours to obtain a super-elastic titanium alloy withα phase finely precipitated.

As yet another embodiment of the present invention a Ti—Mo—Ge alloy isnow described. Effects of Mo added to Ti are the same as described inthe above embodiments.

When Ge is added to Ti, Al functions as an α stabilizer element,extending α phase region so as to improve the strength at roomtemperature. Then, development work has been advanced on super-elastic βsolid solution titanium alloys having the composition of Ti to which Moas a β stabilizer element for lowering martensite transformationtemperature and Ge as an α stabilizer element are added, which undergoesthermo-elastic martensite transformation upon rapid cooling. As aresult, the super-elastic β solid solution titanium alloys with thecomposition mentioned below has been developed.

Mo content as a β stabilizer element is limited within the range of from2 to 12 at %. This is because the super elastic performance isdeteriorated when Mo content is below 2 at % or over 12 at %. In otherwords, there occurs plastic deformation within a deformed alloy, whichmakes it difficult for the alloy to recover its original shape. Asdescribed above, preferable Mo content is within the range of from 4 to7 at %. More preferably, Mo content is within the range of from 5 to 6at %.

Ge content as an α stabilizer element is limited within the range offrom 0.1 to 8 at %. This is because the super elastic performance isdeteriorated when Ge content is below 0.1 at % or over 8 at %. In otherwords, there occurs plastic deformation within a deformed alloy, whichmakes it difficult for the alloy to recover its original shape.Preferable Ge content is within the range of from 1 to 4 at %. Morepreferably, Ge content is within the range of from 2 to 4 at %.

Accordingly, a Ti alloy containing Mo from 2 to 12 at % and Ge from 1 to8 at % becomes a super-elastic β solid solution titanium alloy.Therefore, a crystalline structure of the rapidly cooled titanium alloybecomes orthorhombic with excellent transformation behavior, whichfacilitates hot working and cold working, thereby reducing working costas compared with Ni—Ti alloys.

Such a Ti—Mo—Ge alloy can be manufactured in the same method as that forthe aforementioned Ti—Mo—Al alloy, though the present invention is notlimited to this method. In the other words, metals as given allowingcomponents are melted in a consumable electrode arc melting furnace, andcast into required shapes to prepare ingots. Then, in order to removesegregation, thus prepared ingots are subjected to homogenized heattreatment under the conditions that heat treatment environments arepreferably vacuum or inert gas environments, heat treatment temperaturespreferably range from 1,000 degree to 1,200 degree and the retentiontime is set within the range of from 10 to 48 hours. After beinghomogenized heat treated, the ingots are rapidly cooled down to roomtemperature with the use of oil or water.

The ingots are cold worked to prepare thin sheets. For the purpose ofsolution heat treatment of alloying elements, the thin sheets aresubjected to solution heat treatment under the following conditions thatheat treatment environments are preferably vacuum or inert gasenvironments, heat treatment temperatures preferably range from 600degree to 1,100 degree and retention time is set within the range offrom 1 minute to 10 hours to obtain a super-elastic titanium alloy withα phase finely precipitated.

EXAMPLES Example 1

Ti—Mo—Ga alloy ingots with the compositions shown in Table 1 of FIG. 2were prepared by being melted in a consumable electrode arc meltingfurnace and cast into required shapes. The ingots were subjected tohomogenized heat treatment at a temperature of 1,100 degree for 24 hoursof retention time before the ingots were rapidly cooled down with theuse of water. Then, the ingots were cold rolled to thickness with 95%reduction and prepared to be sheet materials of 0.4 mm in thickness.Test sample of 1 mm in width and 20 mm in length were cut from the sheetmaterials. The test samples were held at 1000 degree for one hour andthen quenched into a water bath, which results in obtainingsuper-elastic titanium alloys.

In order to evaluate shape memory effects of the test samples of thesuper-elastic titanium alloys, the test samples were held at 37 degree,for example by a method of holding them in a constant temperaturechamber. The test samples were bent once to have a single turn around astainless round bar of 10 mm in diameter, and held for 30 seconds whilethey were bent at 180-degree angle. Then, the test samples were takenoff the stainless round bar. After that, bend angles of the resultanttest samples which did not recover their original shapes due to plasticdeformation were measured thereby to evaluate the shape memory effects.

The procedure of measuring a bend angle is described with reference toFIG. 1. When a test sample of a super-elastic titanium alloy 1 which waswound around a stainless round bar is plastically deformed withoutrecovering its original shape, its deformation is expressed by an angle(θ) 2 relative to the horizontal plane.

Evaluation results of the shape memory effects are also shown inTable 1. When the angle (θ) is below 5-degree angle, the alloy isthought to recover its original shape and exhibits the shape memoryeffects, which is denoted by a round mark “∘” in the table. For thenumbers a-7˜a-12 in Table 1, since the compositions are outside of thescope of the present invention, super elastic performance is unfavorableand the original shapes are not recovered. On the other hand, for thenumbers a-1˜a-6 of the present invention, the original shapes arerecovered.

Example 2

Ti—Mo—Al alloy ingots with the compositions shown in Table 2 of FIG. 3were formed into sheet materials of 0.4 mm in thickness in the samemethod as that in Example 1. Test samples of the super-elastic titaniumalloys thus were prepared. Then, shape memory effects of the testsamples of the super-elastic titanium alloys were evaluated in the sameway as in Example 1. Evaluation results of the shape memory effects arealso shown in Table 2. For the numbers b-7˜b-12 in Table 2, since thecompositions are outside of the scope of the present invention, superelastic performance is unfavorable and the original shapes are notrecovered. On the other hand, for the numbers b-1˜b-6 of the presentinvention, the shapes are recovered.

Example 3

Ti—Mo—Ge alloy ingots with the compositions shown in Table 3 of FIG. 4were formed into sheet materials of 0.4 mm in thickness in the samemethod as that in Example 1. The test samples of the super-elastictitanium alloys were thus prepared. Then, shape memory effects of thetest samples of the super-elastic titanium alloys were evaluated in thesame way as in Example 1. Evaluation results of the shape memory effectsare also shown in Table 3. For the numbers c-5—c-10 in Table 3, sincethe compositions are outside of the scope of the present invention,super elastic performance is unfavorable and the original shapes are notrecovered. On the other hand, for the numbers c-1˜c-4 of the presentinvention, the shapes are recovered.

As mentioned above, the inventors of the present invention has achievedthe super-elastic performance expressed within an alloy of the presentinvention which is a titanium-based alloy with Mo and further Ga, Al orGe added thereto. In addition, since an alloy of the present inventionis a nickel-free alloy, the alloy is usable in medical applicationswithout causing allergic problems. In other words, a nickel-free alloyof the present invention having super-elastic performance is alsosuitable for use as materials of medical appliances.

1. A method for making a super-elastic titanium alloy for medical usecomprising the steps of: preparing a titanium alloy ingot which consistsessentially of: molybdenum (Mo) as a β stabilizer element of titanium(Ti) : from 2 to 12 at %; as an α stabilizer element of the titanium(Ti), at least one element selected from the group consisting ofaluminum (Al), gallium (Ga) and germanium (Ge) : from 0.1 to 14 at %;and the balance being titanium (Ti) and inevitable impurities,subjecting the ingot to a homogenized heat treatment in a vacuumenvironment or an inert gas environment at a temperature ranging from1,000 degree to 1,200 degree, and cooling the ingot quickly to a roomtemperature; after cooling the ingot to the room temperature, coldworking the ingot to prepare a sheet; and subjecting the sheet to asolution heat treatment in the vacuum environment or the inert gasenvironment at a temperature ranging from 600 degree to 1,100 degree. 2.The method as claimed in claim 1, wherein the α stabilizer element ofthe titanium alloy ingot is from 0.1 to 14 at % gallium (Ga).
 3. Themethod as claimed in claim 1, wherein the α stabilizer element of thetitanium alloy ingot is from 3 to 14 at % aluminum (Al).
 4. The methodas claimed in claim 1, wherein the α stabilizer element of the titaniumalloy ingot is from 0.1 to 8 at % germanium (Ge).
 5. The method asclaimed in claim 1, wherein a content of the molybdenum (Mo) is from 4to 7 at % and the α stabilizer element of the titanium alloy ingot isfrom 3 to 9 at % aluminum (Al).
 6. The method as claimed in claim 1,wherein a content of the molybdenum (Mo) is from 4 to 7 at % and the αstabilizer element of the titanium alloy ingot is from 1 to 4 at %gallium (Ga).
 7. The method as claimed in claim 1, wherein a content ofthe molybdenum (Mo) is from 4 to 7 at % and the α stabilizer element ofthe titanium alloy ingot is from 1 to 4 at % germanium (Ge).
 8. Themethod as claimed in claim 1, wherein a time of the homogenized heattreatment ranges from 10 to 48 hours.
 9. The method as claimed in claim1, wherein a time of the solution heat treatment ranges from 1 minute to10 hours.